A cellular wireless system typically includes a number of base stations that are configured to provide wireless coverage areas, such as cells and cell sectors, in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices (whether or not user operated), can operate. In turn, each base station could be coupled with a core network having nodes that that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the system could engage in air interface communication with a base station and could thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Such a system could operate in accordance with a particular radio access technology, with air-interface communications from the base stations to UEs defining a downlink or forward link and air-interface communications from the UEs to the base stations defining an uplink or reverse link.
In accordance with the radio access technology, each coverage area could operate on a carrier, which could be frequency division duplex (FDD), defining separate frequency channels for downlink and uplink communication, or time division duplex (TDD), with a single frequency channel multiplexed over time between downlink and uplink use. Further, on the downlink and uplink, the carrier could be structured to define various physical channels for carrying information between the base stations and UEs. For example, the air interface could be divided over time into frames, with each frame being divided in turn into subframes and timeslots, and the carrier bandwidth could be divided over frequency into subcarriers, which could be grouped within each timeslot to define physical resource blocks (PRBs) in which the subcarriers can be modulated to carry data.
Over the years, the industry has embraced various generations of radio access technologies, in a continuous effort to increase available data rate and quality of service for end users. These generations have ranged from “1G,” which used simple analog frequency modulation to facilitate basic voice-call service, to “4G”—such as Long Term Evolution (LTE), which facilitates mobile broadband service using technologies such as orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO). And most recently, the industry is now exploring developments in “5G” and particularly “5G NR” (5G New Radio), which may use a scalable OFDM air interface, advanced channel coding, massive-MIMO, beamforming, and/or other features, to support higher data rates and countless applications, such as mission-critical services, enhanced mobile broadband, and massive Internet of Things (IoT).